It is common to provide magnetic tape write/read head assemblies having one or more write/read transducer heads positioned transverse to the intended path of a magnetic recording medium, i.e., tape, for writing data on and reading data from parallel tracks on the tape. It is also known to include servo information on at least some of the tracks and provide servo transducer heads for reading such information to enable control of the lateral position of the head assembly, thereby dynamically maintaining the respective transducer heads of the head assembly relative to tape tracks. With the use of servo control, data track widths can be made significantly narrower and the capacity of the recording medium can therefore be increased.
Various techniques for providing the servo information contained in tracks, i.e., servo tracks, have been previously employed. For example, it is known to provide dedicated servo tracks on the medium at the time of manufacture. However, it is desirable to enable an end-user to write a servo pattern on the medium in the field as opposed to factory writing of servo information. This allows the end-user to add the servo information to either a blank medium or utilize a medium which was either intentionally or unintentionally erased.
There are a substantial number of different servo track configurations for providing servo control. For example, some of the different configurations are generally characterized by the utilization of either alternating information containing tracks embedded on an erased band and a single head or a center tapped head, as shown in FIG. 1, or alternating tracks with different distinguishable characteristics such as one or more discrete monofrequencies and a single head or a center tapped head, such as shown in FIG. 2. As shown in FIG. 1, a single servo transducer 14 is utilized for sensing servo information on the alternating servo tracks 12 in servo band 10 on an erased background for use in positioning data heads 19 within the data bands 18. Alternatively, a center tapped head 16 may be utilized for providing position error signals as a function of the position of the head 16 over the tracks 12 within the servo band 10.
As shown in FIG. 2, a single servo head 24 may be utilized for providing servo information from alternating servo tracks 22 within servo band 20 having different distinguishable characteristics. The information is then used to position the data heads 29 correctly within the data bands 28 for performing read and/or write functions. Alternatively, a center tapped head (or two servo transducer elements) 26 may be utilized to generate a position error signal from the servo information recorded within the servo band 20.
However, these different servo configurations have ambiguity associated with identifying which servo track is being used for deriving the position error signal to provide for servo control of the system. Although the servo track provides adequate positioning information, it does not provide any information as to which servo track the servo head is currently utilizing to generate the position error signal for servo control. Therefore, if the servo transducer is unintentionally repositioned, a misidentification of the servo track being used for servo positioning of the data read/write heads occurs.
Various configurations attaining some improvement with respect to the above configurations are shown in FIGS. 3, 4, and 5, wherein multiple heads are utilized for generating positioning information from the servo information written in the servo band. As shown in FIG. 3, multiple heads 32 are utilized for reading servo information from a servo track 34 recorded in servo band 30 for positioning data heads 36 within the data bands 38. Further, as shown in FIG. 4, multiple servo heads 42 are utilized for reading servo information from a pair of distinguishable servo tracks 44 within servo band 40 to position data heads 46 within data bands 48.
The above configurations either rely on a single servo track utilizing multiple servo heads (wherein the number of heads is at least N-2 and N is the number of data tracks in a data band), rely on a pair of distinguishable servo tracks which also requires the use of at least N-2 servo heads, or rely on a set of alternating distinguishable tracks which fill the servo bands. With the use of multiple heads and a single servo track or a pair of distinguishable servo tracks (FIGS. 3 and 4), an undesirable large number of servo heads is necessary. With regard to the latter multiple alternating distinguishable tracks, such tracks are very difficult to write in situ in a tape drive.
For example, in writing multiple distinguishable tracks, servo write heads may not be placed adjacent to one another. Therefore, when servo tracks are written contiguous with one another as in the pair of alternating distinguishable servo tracks (FIG. 4) and set of multiple alternating distinguishable servo track (FIG. 2) configurations, it is required that they be written on multiple passes or with heads along multiple gap lines. For precision writing, this typically requires that the pattern be written in the factory. In many cases it is desirable to write servo information in the field. Further, although with the use of multiple alternating distinguishable tracks written across the servo band, the number of servo heads necessary is reduced to one or two heads, the problem of ambiguity in servo track identification is still applicable.
In another servo configuration which utilizes multiple spaced heads as shown in FIG. 5 (extracted from U.S. Pat. No. 5,262,908, to Iwamatsu et al., issued Nov. 16, 1993), multiple heads 52 are utilized for reading information from a plurality of spaced servo tracks 54 within servo band 50 for positioning data read/write heads 56 within data bands 58. However, with respect to such a configuration and the other configurations as described above which use multiple servo heads, it is difficult to produce head assemblies that include such multiple servo heads. Particularly, in thin film heads, limited space is allotted between adjacent data bands and therefore, space is limited for the leads from each of the multiple servo heads. In high track density heads, such leads are much larger than the width of the track pitch. As such, production of such multiple heads in the head assembly in such thin film heads is difficult.
For the above reasons and other reasons that will be apparent from the description below, alternatives to the configurations such as those described above are needed to overcome difficulties associated therewith. For example, the unambiguous identification of individual servo tracks is desired. Further, it is desired to reduce the number of servo heads necessary for providing servo control and also it is desirable to write servo tracks in the field in a single pass.